A video can be a display of sequential static images shown in rapid succession such that the human brain perceives the changes from one static image to the next as continuous movement. For example, motion pictures (i.e., movies) are often displayed at twenty four or forty eight frames per second. Video for television is often displayed at fifty frames per second, sixty frames per second, or multiples thereof.
Video projectors project a light source onto an imaging circuit (e.g., a liquid crystal display (LCD), liquid crystal on silicon (LCoS), or Digital Light Projection (DLP®)) to form an image and then project the image onto a surface (e.g., a display screen). Video projectors often use a shutter mechanism to shorten the time that individual sequential static images are presented to a viewer's eyes.
The shutter can also reduce motion blur perceived by a viewer. If a projected image of an object is moving across a projected image field (e.g., a baseball traveling through the air or an aircraft flying across the screen), a viewer's eye will attempt to smoothly track the perceived moving object. However, as described above, the projected image of the moving object is actually a sequence of static images. Thus, when the shutter is open during display of any one particular static image, the object is not moving. Consequently, during the brief period of time that any particular static image is displayed, the viewer's eye is moving to track the object while the object is static. As a result, the projected image is “smeared” across the viewer's retina such that the viewer perceives a blurry image.
To counteract image blur, the amount of time that the shutter is open can be decreased. By decreasing the open shutter time (i.e., the duty cycle), each static image is displayed for a shorter period of time, which reduces the “smearing” of the image on the retina as the viewer's eye attempts to track a moving object. However, decreasing the duty cycle also decreases the brightness of the displayed image.
Additionally, video images are often displayed according to a particular color specification. The specification assumes that a light output from a projector has a particular color temperature (i.e., white point) when the projector responds to the full scale input for each of the input primary colors (usually red, green, and blue). However, the projector may not output the correct color temperature when outputting at full brightness. The color temperature may be corrected by attenuating one or more of the primary colors from the light output, but such correction decreases the brightness of the displayed image.